1. Field of the Invention
The present invention relates to an optimized textile weave, of the linked multilayer type, which can be used in the production of composite material components which are highly stressed and/or subjected to impacts. By way of example, such components include wide-chord fan blades for civil aircraft engines, structural casing arms for civil or military aircraft engines, and self-stiffened aircraft panels or leading edges.
The subject of the invention is therefore a woven fibrous fabric, constituting a textile preform for the production of such components, which may be preimpregnated by means of liquid, for example using the "RTM" (Resin Transfer Moulding) injection process, or by means of gas. For this purpose, the textile preform must satisfy a number of criteria or conditions:
the use of fibres which have very high mechanical performance characteristics but which a priori are brittle during weaving, such as high-modulus carbon fibres; PA1 the use of carbon fibres having an unusual and high linear density, for example consisting of 48 or 96 kilofilaments, or even more; PA1 the optimum degree of interlinking in the thickness direction of the fabric; PA1 the possibility of producing composite materials having a high volume fraction filled by fibres, in particular a fraction of greater than 57% for structural composite materials; PA1 linearity of the weft yarns in the fabric; PA1 a low linkage angle (in particular less than 15.degree.) between the warp yarns and the weft yarns and the possibility of unbalanced weaving so as to compensate for the non-linearity of the warp yarns and to adjust the properties in the plane of the fabric, (for example, with a proportion of 70% warp yarns and 30% weft yarns); PA1 the possibility of reversing the unbalanced weaving (by rotating the weave through 90.degree.) so as to improve the linearity; and PA1 the formation of a linked fabric which is highly deformable. PA1 a first of said at least three parallel warp yarns connects the upper outermost weft yarn of one of said columns containing at least four weft yarns to an upper intermediate weft yarn of a second column of at least four weft yarns spaced from said one column by at least twice said predetermined spacing, and returns to the upper outermost weft yarn of a column containing at least four weft yarns spaced from said one column by at least four times said predetermined spacing; PA1 a second of said at least three parallel warp yarns connects an upper intermediate weft yarn of said one column to a lower intermediate weft yarn of said second column, and returns to an upper intermediate weft yarn of said column of at least four weft yarns which is spaced from said one column by at least four times said predetermined spacing; and PA1 a third of said at least three parallel warp yarns connects a lower intermediate weft yarn of said one column to the lower outermost weft yarn of said second column, and returns to a lower intermediate weft yarn of said column of at least four weft yarns which is spaced from said one column by at least four times said predetermined spacing;
2. Summary of the Prior Art
So-called "1D" and "2D" textile structures, depending on whether their fibres extend in a single direction or in two different directions, do not satisfy the abovementioned constraints. So-called "3D" multilayer structures (having fibres arranged along three directions in space) may approach, at least partly, the desired objectives in the field of application of the invention. However, with regard to multilayer structures having more than three fibre directions ("4D", "5D", "9D", "11D", these cannot be exploited on an industrial scale because of the extreme complexity of their production using automatable processes.
Thus, we shall look in more detail at multilayer structures of the "3D" type.
Among these structures, stitch-linked "3D" multilayer fabrics are known which fully meet the linearity of the warp yarns and which have the advantage of including reinforcing yarns at other angles. However, this method of linking does not make it possible to impart good impact resistance to the composite materials obtained.
Also known are "3D" multilayer fabrics linked by weaving, the orthogonal "3D" fabric being the weave which has the best linearity of warp and weft yarns and which resists compression well. However, in order for this fabric to provide the desired volume fraction of fibres, the "3D" fabric must be compressed in such a way that the yarns arranged along the third direction, which are corrugated rather than linear, do not contribute to load transfer.
Although "non-orthogonal 3D" multilayer fabrics are more suitable, they have the drawback of having linkage angles which are too high, this being the case for simple weaves of the multilayer taffeta, multilayer satin or multilayer twill type, and also more elaborate weaves, such as that known by the name "3X".
The particular fabric of the "non-orthogonal 3D" type, also known as "2.5D", described in FR-A-2,610,951 is the weave known hitherto to be the most optimized, having a low expansion and a high percentage of surface occupied, but with a low linearity. However, the restrictive definition of this fabric gives it angular characteristics prejudicial to the impact strength and limits the reversible textile definitions (by rotation of the weave through 90.degree.) to constructions of low density, unless a high number of additional layers is added, which is prejudicial to industrial automation.